(2015/01/14 17:47), Jiri Kosina wrote:
> Using IPMODIFY needs to be allowed only with compilers which are
> guaranteed to generate function prologues compatible with function
> redirection through changing instruction pointer in saved regs.
>
> For example changing regs->ip on x86_64 in cases when gcc is using mcount
> (and not fentry) is not allowed, because at the time mcount call is
> issued, the original function's prologue has already been executed, which
> leads to all kinds of inconsistent havoc.
>
> There is currently no way to express dependency on gcc features in
> Kconfig, (CC_USING_FENTRY is defined only during build, so it's not
> possible for Kconfig symbol to depend on it) so this needs to be checked
> in runtime.
>
> Mark x86_64 with fentry supported for now. Other archs can be added
> gradually.
>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> ---
>
> v1 -> v2: turn macro function into a plain macro
>
> arch/x86/include/asm/ftrace.h | 2 ++
> include/linux/ftrace.h | 5 +++++
> kernel/trace/ftrace.c | 5 +++++
> 3 files changed, 12 insertions(+)
>
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index f45acad..f84eaaf 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -4,8 +4,10 @@
> #ifdef CONFIG_FUNCTION_TRACER
> #ifdef CC_USING_FENTRY
> # define MCOUNT_ADDR ((long)(__fentry__))
> +# define ftrace_ipmodify_supported 1
> #else
> # define MCOUNT_ADDR ((long)(mcount))
> +# define ftrace_ipmodify_supported 0
> #endif
> #define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 1da6029..837153a 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -244,6 +244,11 @@ static inline int ftrace_function_local_disabled(struct ftrace_ops *ops)
> extern void ftrace_stub(unsigned long a0, unsigned long a1,
> struct ftrace_ops *op, struct pt_regs *regs);
>
> +#ifndef ftrace_ipmodify_supported
> +/* let's not make any implicit assumptions about profiling call placement */
> +# define ftrace_ipmodify_supported 0
> +
> +#endif
> #else /* !CONFIG_FUNCTION_TRACER */
> /*
> * (un)register_ftrace_function must be a macro since the ops parameter
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 929a733..05af4cd 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1809,6 +1809,11 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
> if (!(ops->flags & FTRACE_OPS_FL_IPMODIFY))
> return 0;
>
> + if (!ftrace_ipmodify_supported) {
> + WARN(1, "Your compiler doesn't support features necessary for IPMODIFY");
> + return 0;
> + }
> +
Hmm, if this binary doesn't support IPMODIFY, it should return -ENOTSUPP.
And also, IMHO, we'd better reject registering ftrace_ops with IPMODIFY
in this situation before updating hash table.
Thank you,
> /*
> * Since the IPMODIFY is a very address sensitive action, we do not
> * allow ftrace_ops to set all functions to new hash.
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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